I have three 12v lead acid batteries for my 112 Ultrex. As one or more of them begin to age/fail... can I swap the bad one out for a 100ah Lithium battery that I already own? Or would I need to change all 3 lead acid batteries out for 3 lithium? I also currently have a MinnKota bank charger for the lead acid batteries. What charger would be recommended for 1-3 lithium batteries? 
 

 

They are expensive, But in long run they are worthy. The question I have is about Gel batteries for trolling motor. Anyone have any experience with them?

38 minutes ago, ATA said:

They are expensive, But in long run they are worthy. The question I have is about Gel batteries for trolling motor. Anyone have any experience with them?

I had a gel in my old runabout - for the minor difference in price between Gel and AGM...go with the AGM, it's better all around.

I'm no expert but I'd change all 3. They charge and discharge at different rates then flooded.

 

Noco makes top of the line lithium chargers.  The manufacturer of the lithium may have suggestions on a charger too.

It’s best to combine batteries of the same type and age.  Combining lithium and lead acid is a very bad idea.  

28 minutes ago, Tennessee Boy said:

It’s best to combine batteries of the same type and age.  Combining lithium and lead acid is a very bad idea.  

^ This - you don't even want to combine different types of Lead-Acid.

 

If you go flooded - make them all flooded

Same with Gel and AGM - do NOT mix types.

 

And as already stated, you want to try your best to match age/capacity as well.

If you're going 36v - then all three should be the same AH rating - and buying all the same brand/model is a very good idea.

As already stated don’t run different batteries. As for you charger if it’s a MinnKota Precision or Digital you’ll be fine to use on some lithiums. The manufacturer can tell you if there batteries are compatible with what chargers. I run Ionic LiFePo4 lithiums and my Precision 4 bank work great.